Yes, am using the correct deluxe/custom horn (for a 66). In my case I installed a 1970 steering column in my 64. I just like the looks of the 66 horn.
That said, me and my neighbor figured it out yesterday. Seems I was missing a piece. After we made one it worked like a champ.
I did take pics;
This is the order of assembly photo. On the paper is the orientation of the parts (note the direction of the concave flex plate).
http://s307.photobucket.com/user/Ru...tion_zps67877178.jpg.html?sort=3&o=3

This is the correct isolator and the dimension it is.
http://s307.photobucket.com/user/Ru...tors_zps09b84660.jpg.html?sort=3&o=2

This is the part that I was missing (kept the whole thing from working). I used an existing standard horn piece and cut it down.
http://s307.photobucket.com/user/Ru...iece_zps3a61291c.jpg.html?sort=3&o=1